JPH01169725A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a disk-shaped magnetic recording medium which is uniform in the degree of orientation in a circumferential direction while eliminating the influence of mechanical orientation by passing a high strip coated with a magnetic coating compd. in an undried state near members for random orientation arrayed alternately with S poles and N poles so that said strip is subjected to non-orientation, then subjecting the strip to magnetic orientation in the circumferential direction. CONSTITUTION:A base film 4 which is coated with the magnetic coating compd. in the undried state traveles in the rotating direction of supporting films 1a, 1b, i.e., from the right to the left and are subjected to the non-orientation by random orienting devices 2a, 2b during the course of such travel. The random orienting devices 2a, 2b are disposed with micromagnets in such a manner that the S poles and N poles array on the roll surfaces and these rolls rotate in the traveling direction of the base film 4. The upper and lower rolls of the random orienting devices 2a, 2b are synchronized with each other so that the same magnetic poles face each other above and below at all times. The raw sheet 4 subjected to the non-orientation by the magnets 2a, 2b for random orientation is circumferentially oriented by the opposed circumferentially orienting magnets in succession to the above.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a disk-shaped magnetic recording medium suitable for high-density recording.

[Conventional technology]

In recent years, flexible disk-shaped magnetic recording media have been widely used, such as flexible disks used as large-capacity storage devices for computers and magnetic sheets for still video cameras.

However, when using this type of magnetic recording medium, the magnetic head slides along the circumference to read and write records, whereas normally manufactured magnetic recording media Because the magnetic powder that forms the layer is not oriented in a circumferential manner, the squareness ratio is poor and the residual magnetization is lower than that of a magnetic tape in which the magnetic powder is oriented. Therefore, in this disk-shaped magnetic recording medium, there is an effect of widening the track width in order to obtain sufficient output, which hinders high density.

In addition, when using needle-like magnetic powder with a large axial ratio, such as those normally used in tapes, it is possible to avoid using an orientation device during the coating and drying process in the coating direction of the non-magnetic support sheet (e.g. Even if a signal with a constant amplitude is recorded circumferentially on a disk-shaped punched disk, the residual magnetization is larger in the longitudinal direction.
There was also the problem that the envelope waveform was not constant and the output fluctuated periodically.

[Problems to be solved by the invention] Therefore, in the currently dominant floppy disks and video floppies, the mechanical orientation is weakened during the coating process, or magnetic powder with a small axial ratio is used to make the envelope as narrow as possible. I try to keep it flat. However, such a method suppresses the original characteristics of the acicular magnetic powder. This point will be clarified by comparing it with metal tape.

The axial ratio of the metal magnetic powder of the metal tape can be selected from about 5 to 11, but usually about 7 to 9 is used. The squareness ratio of a tape using such long needle-shaped magnetic powder is about 0.55 in the case of no orientation, but becomes about 0.6 to 0.65 when mechanical orientation is added. Furthermore, as disclosed in Japanese Patent Publication No. 34-2536, magnetic field orientation is imparted using a device in which a sheet coated with magnetic paint before solidification is passed between two plate magnets with the same magnetic poles facing each other. For example, the squareness ratio increases to about 0.8 to 0.85. −
Magnetic powders with numerically larger shape anisotropy, that is, larger axial ratios, are more likely to be mechanically oriented, and as a result of orientation, a larger squareness ratio can be obtained. On the other hand, a metal video floppy whose orientation is suppressed has a squareness ratio in the circumferential direction of about 0.6 to 0.65, which lowers the output by about 3 dB when compared with tape.

Remove mechanical orientation before application, such as circumferential (concentric circles)
Many methods have been proposed in the past for orientation. For example, Japanese Patent Publication No. 40-23626 discloses a method of circumferentially orienting by an externally applied magnetic field. In this method, in a state where the magnetic paint is not solidified, the rotating magnetic pole surfaces are kept stationary relative to the rotational axis of the original material, the magnetic pole surfaces are brought close together, the magnetic powder is oriented concentrically, and then separated. It is something. In the example of this method, a rotating magnetic field is applied from one side of the original material, but in the case of a tape, as shown in Japanese Patent Publication No. 34-2536, in the case of a disk, it is applied from the opposite side. It is better to install a rotary 1if 1-pole surface having the same magnetic pole on the opposite side across the original fabric. A conceptual diagram of such a device is shown in Japanese Unexamined Patent Publication No. 53-62505.

In these orientation methods using a rotating magnetic field, the magnetic field orientation force is
Basically, it is the same at any position on the circumference. On the other hand, as mentioned earlier, the mechanical orientation force is strong in the direction of fabric running, so even after applying the magnetic field orientation, the orientation in the direction parallel to the running direction of the fabric is perpendicular to the running direction within the plane of the fabric. Differences in orientation in the direction remain. As a result, the squareness ratio at any position in the circumferential direction of a disc-shaped magnetic recording medium obtained by the conventional orientation method is 0.75 to 0.8, and the squareness ratio obtained by longitudinal direction orientation in the case of magnetic tape, etc. is 0.75 to 0.8. squareness ratio (0
, 8 to 0.85) and are not sufficiently oriented. This is extremely difficult because in order to orient the ferromagnetic particles aligned in the longitudinal direction in the circumferential direction by mechanical orientation, the ferromagnetic particles must be rotated up to 90' in the width direction of the ribbon. It's for a reason. An object of the present invention is to provide a disk-shaped magnetic recording medium which has a constant degree of orientation in the circumferential direction without being affected by mechanical orientation, and has a degree of orientation as high as the longitudinal direction orientation in a magnetic tape.

[Means for Solving the Problems] The above purpose is to apply a magnetic paint containing magnetic powder onto a running wide thin non-magnetic support, and after drying it to form a magnetic layer. In a method for manufacturing a magnetic recording medium punched into a disk shape, the thin strip coated with magnetic paint and before being dried and solidified is passed near a random orientation member in which S poles and N poles are arranged alternately. This can be achieved by a method for manufacturing a disk-shaped magnetic recording medium, which comprises the steps of making the magnetic particles in the magnetic paint non-oriented and then magnetically orienting them in a circumferential manner.

The present invention disorderizes the orientation of the magnetic paint in an unsolidified state, removes the mechanical orientation, and then applies a circumferential orientation magnetic field. This method produces a disk-shaped magnetic recording medium with the same degree of orientation at both sides, and thereby increases the degree of orientation to the same level as that of a magnetic tape oriented by a magnetic field in the longitudinal direction.

In particular, the above-mentioned member that provides magnetic non-orientation can be easily installed and can handle high line speeds.

In the present invention, the step of making the magnetic coating material non-oriented is important, and an example of an apparatus used for this purpose is shown in FIGS. 1 and 2, respectively. The apparatus of FIG. 1 has supporting rolls la, l.
b and random orientators 2a and 2b. The undried base film 4 coated with magnetic paint is moved by the support rolls la and lb in the rotational direction of the support rolls 1a and 1b, that is, from right to left in the drawing.

The random orientators 2a and 2b have an S pole and an N pole on the roll surface.
Micro magnets are arranged so that the poles are arranged alternately.

This roll rotates in the running direction of the base film. Also, a random orientator 2a.

The upper and lower rolls of 2b are synchronized with each other, and the same upper and lower magnetic poles always face each other.

FIG. 2 shows random orientators 3a and 3b of a type in which random orienting magnets are arranged on a belt.

FIG. 3 is a surface development view of an example of a random orientator,
It shows the arrangement of micromagnets and the pattern of the magnetic field.

The magnetic field strength of the random orientation magnet is preferably 20 to 2000 oersted, more preferably limited to 10 to 100% of the coercive force of the magnetic powder used. The speed of the roll or belt can be chosen arbitrarily, but better results will be obtained if it is slightly faster than the speed of the base film. Further, the random orientation magnet has the greatest effect when placed above and below the base film, but a considerable effect can be obtained even when placed either above or below the base film.

FIG. 4 is a side view showing an example of a magnetic field orientation device used in the present invention. The conveyance rolls 1a and 1b carry the raw material 4, which has the magnetic paint coated on the base film and is not solidified.
It can be moved at a constant speed in the direction of arrow 13.

The rotating drum 11 holding the circumferentially oriented magnets 5a, 5b, 5C, .
It rotates at a constant circumferential speed that is synchronized with the web running speed.

Circumferentially oriented magnets 6a, 6b, 6 are arranged symmetrically across the original fabric 4.
A rotating drum 12 that holds C... is provided,
This also rotates around the rotating shaft 9 in the direction of the arrow 10 at the same circumferential speed as the rotating drum 11 . Rotating drum 11.12
Random orientation magnets 2a and 2b are provided at the front.

When this device is operated, the original fabric 4 is transferred to the conveyor rollers la, l.
b and is sent between the random orientation magnets 2a and 2b to be non-oriented. Subsequently, the raw web 4 that has passed between the rotating drums 11.12 is oriented in a circumferential manner by the opposing circumferential orientation magnets 5.6.

In the example shown in FIG. 4, the circumferential orientation magnet was held on a rotating drum and rotated, but as shown in FIG.
．． 15 may be held and conveyed. In this case, the circumferentially oriented magnet 5.6 can maintain a stopped state relative to the original web 4 for a longer time.

It should be noted that either a permanent magnet or an electromagnet can be used as the circumferentially oriented magnet 5.6. Further, these circumferentially oriented magnets can be used either in a method using rotating magnetic poles or a method using fixed magnetic poles. However, those that achieve the same purpose,
That is, it is not limited to these as long as it can form a circumferential magnetic field. Further, in the examples shown in FIGS. 4 and 5, a circumferential orienting magnetic field of the same magnetic pole is applied from both sides of the original fabric, but the orientation effect of the present invention can be obtained even if it is applied only from one side.

In the present invention, the magnetic field for one circumferential orientation is usually 1000 to 5
It may be about 000 0e.

[Example] Acicular magnetic metal powder (Fe-Ni alloy, long diameter ○ 25μ
, axial ratio 10, HCl 4500e), 25 parts of binder (6:4 mixture of vinyl chloride-vinyl acetate-vinyl alcohol copolymer and polyurethane elastomer), 1 part by weight of lecithin (dispersant), α - 10 parts by weight of alumina (abrasive, particle size 0.4 μm) and 2
A magnetic paint obtained by dispersing and mixing 40 parts by weight of a solvent (a 1=1 mixture of methyl ethyl ketone and toluene) was applied onto a PET base to a dry thickness of 3 μm.

Next, using the apparatus shown in FIG. 5, the orientation treatment was performed as described above, and punching was performed to obtain a disk-shaped magnetic recording medium (diameter: 47 m).
m).

Note that random orientation magnets are made by forming an axis on a ribbon as shown in Figure 3, and winding the ribbon around a roll (first
(Fig. 2) and one in which the ribbon was run like a belt conveyor (Fig. 2) were used (the results were the same in either case).

The magnetic field strength of each magnetic domain was set to 7000e, and the circumferentially oriented magnet was set to 30000e.

Comparative Example 1 A disc-shaped magnetic recording medium was produced in the same manner as in Example 1, except that no orientation by a magnetic field was performed.

Comparative Example 2 A disk-shaped magnetic recording medium was produced in the same manner as in Example 1, except that non-orientation was not performed.

Comparative Example 3 A disk-shaped magnetic recording medium was produced in the same manner as in Example 1, except that circumferential orientation was not performed.

Example 2 A magnetic recording medium was produced in the same manner as in Example 1 except that the random orientation magnet was replaced with 10000e.

(evaluation) Characteristics such as squareness ratio and residual magnetization of Examples and Comparative Examples were investigated.

The results are shown in Table 1.

From this table, the effect of the present invention can be clearly confirmed.

[Effects of the Invention] As explained above, according to the manufacturing method of the present invention, the degree of orientation is constant in the circumferential direction with almost no influence of mechanical orientation, and the degree of orientation is as high as the longitudinal direction orientation in magnetic tape. A disk-shaped magnetic recording medium having a high squareness ratio and a high squareness ratio can be obtained.

[Brief explanation of the drawing]

FIGS. 1 and 2 are schematic diagrams of an example of a device for performing random orientation, FIG. 3 is a developed surface diagram of an example of a random orientation device, and FIGS. 4 and 5 are diagrams of the present invention, respectively. FIG. 2 is a schematic side view showing an example of an orientation device used for. la, lb: Conveyance rollers 2a, 2b, 3a, 3b: Random orientator 5a15b1
5C..., 6a, 6b, 6cm...: Circumferential oriented magnet 7.9: Rotating shaft 8.10: Rotating direction 11.12: Rotating drum 13: Original fabric running direction 14.15: Belt conveyor or caterpillar shape Patent applicant for orientation magnet holding device Canon Co., Ltd.

Claims (1)

[Claims] 1) A method of manufacturing a magnetic recording medium by applying a magnetic paint containing magnetic powder onto a running wide thin non-magnetic support, drying it to form a magnetic layer, and then punching it out into a disk shape. In this process, the thin strip coated with magnetic paint but before being dried and solidified was passed near a random orientation member in which S and N poles were arranged alternately, so that the magnetic particles in the magnetic paint were rendered non-oriented. 1. A method for manufacturing a disk-shaped magnetic recording medium, the method comprising: a step of magnetically orienting the medium in a circumferential manner;